The term broadband covers a host of new products, technologies, services, and networks. One way to define broadband networks is to categorize them as those networks that support services requiring bit rates well above one megabits per second. Business and residential subscribers will be connected to broadband networks via a common access, operating at 150 megabits per second or above, that can handle a range of different broadband service types. ATM (asynchronous transfer mode) has been chosen as the communication principle on which broadband networks will be based. A future broadband ISDN (integrated services digital network) will offer the flexibility needed to handle diverse services ranging from basic telephone service to high speed data transfer, videotelephony, and high quality television distribution. The key to this flexibility is ATM which carries digital information in special cells. This allows the network to be used efficiently by applications and services with widely differing bandwidth requirements and call characteristics.
A growable packet switching arrangement disclosed in a paper by K.Y. Eng et al., entitled "The Growable Switch Architecture: A Self-Routing Implementation for Large ATM Applications", International Conference on Communications, June 1991, has been proposed for use in ATM applications. In the disclosed arrangement, a partition is made between a front-end distribution network and a column of output packet switching modules. The outputs are divided into groups of n lines each. All incoming cells are routed through the front-end distribution network for substantially instantaneous delivery based on their destination output group addresses. As such, the distribution network must not buffer full cells and must instead perform its routing function for all the cells arriving in each packet time slot. Since the n outputs are grouped into n lines each, there are a total of N/n output groups. For each output group, the corresponding output packet switching module has m (m&gt;=n) inputs, meaning that up to m cells can be accepted for that output group in each time slot. The output packet switching module has buffers for storing full received cells. In an L.times.N packet switch, up to L cells can arrive simultaneously for a particular output group so the design range of m is n&lt;=m&lt;=L. According to the generalized knockout principle, it is possible to pick m&lt;&lt;N to yield an arbitrarily small cell loss probability that is acceptable for the switching system design, even under the most general traffic assumptions. The maximum number of cells accepted into each output group is restricted to m; if there are more than m cells destined to the same output group in a time slot, the excessive cells are simply dropped. Although the general characteristics of a growable packet switching arrangement are known, the design of such an arrangement with a low cost, high performance distribution network remains an important problem.
A high performance, self-routing ATM switch, referred to as a rerouting network (FIG. 39) is disclosed in a paper by S. Urushidani entitled, "Rerouting Network: A High-Performance Self-Routing Switch for B-ISDN", IEEE Journal on Selected Areas in Communications, Vol. 9, No. 8, Oct. 1991. Although the Urushidani paper contains no disclosure, teaching or suggestion concerning growable packet switching arrangements, the performance of the disclosed ATM switch is enhanced by a "rerouting" algorithm applied to a particular multistage interconnection algorithm. The interconnection algorithm offers many access points to the output and resolves output contention by including buffers at each switching stage. The rerouting network is a multistage interconnection network with more than log.sub.2 L switching stages. The stages are interconnected by routing links and bypass links. The algorithm is applied to embed plural banyan networks within the switch. That is, the partial networks composed of switching elements and routing links from switching stages 1 to 4, from 2 to 5, and so on are banyan networks, because a single path always exists between all input-output pairs. Therefore, a cell that fails to take its desired route due to cell contention at a given stage can restart its routing from the next stage through a banyan network formed in the following log.sub.2 L stages. This restart is referred to as "rerouting". On the other hand, the bypass links route the cell, having reached its destination, to the output line without switching at each switching element. Although the rerouting network has good performance--for example, relatively low blocking-it is not suitable for use as the distribution network of a growable packet switching arrangement. One of the key properties of a growable packet switching arrangement is that the nodes of the distribution network should not be required to buffer full packets. The rerouting network nodes each include sufficient buffers to store full 53-byte ATM cells for later transmission. Accordingly, the nodes are complex and expensive in sharp distinction to the distribution network nodes needed in a growable packet switching arrangement.
In view of the foregoing, a need exists in the art for a growable packet switching arrangement with a low cost, high performance distribution network.